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CSS

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HTML 

              
                 <!-- tabs -->
    <div class="input-settings">
      <ul class="tabs">
        <li class="tab digits active">
          <span class="title">Digits</span>
        </li>
        <li class="tab letters">
          <span class="title">Letters</span>
        </li>
        <li class="tab yours">
          <span class="title">Yours</span>
        </li>
        <div class="slider"></div>
      </ul>
    </div>
    <!-- END tabs -->

    <!-- custom regular expression input -->
    <div class="my-reg-ex-container">
      <input class="my-reg-ex" type="text" />
    </div>
    <!--END custom regular expression input -->

    <!-- input -->
    <input class="primary" type="text" />
    <!--END input -->

    <!-- made in jssecrets.com -->
    <a class="jssecrets" href="https://jssecrets.com/" target="_blank"
      >jssecrets.com</a
    >
    <!-- made in jssecrets.com -->
!

CSS 

              
                @import url("https://fonts.googleapis.com/css2?family=Poppins:wght@400;500;800&display=swap");
@import url("https://fonts.googleapis.com/css2?family=Urbanist:wght@500&display=swap");
*,
::before,
::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: "Poppins", sans-serif;
}

ul {
  list-style: none;
}

body {
  height: 100vh;
  background: hsl(225, 14%, 12%);
  position: relative;
  display: flex;
  justify-content: center;
  align-items: center;
  overflow: hidden;
  color: #292d34;
}

input.primary {
  width: 320px;
  border: 2px solid rgb(80, 121, 247);
  box-shadow: 0 4px 20px rgba(80, 121, 247, 0.4);
  color: rgb(80, 121, 247);
  background: transparent;
  outline: none;
  font-size: 24px;
  padding: 16px;
  border-radius: 12px;
  transition: all 0.8s ease-out;
  opacity: 1;
}
@media (max-width: 400px) {
  input.primary {
    width: 220px;
    padding: 8px;
  }
}

.input-settings {
  width: 320px;
  border-radius: 10px;
  background-color: hsl(225, 14%, 17%);
  border: 1.5px solid rgba(0, 0, 0, 0.38);
  box-shadow: 0 8px 32px 0 hsl(225, 14%, 12%);
  backdrop-filter: blur(40px);
  padding: 16px;
  position: absolute;
  left: 50%;
  top: 5%;
  transform: translate(-50%, -5%);
  opacity: 1;
  transition: all 0.7s ease-out;
}
@media (max-width: 400px) {
  .input-settings {
    width: 220px;
    padding: 8px;
  }
}

.my-reg-ex-container {
  position: absolute;
  left: 50%;
  top: 21.4%;
  transform: translate(-50%, -5%);
  width: 320px;
  transition: all 0.5s ease-out;
}
@media (max-width: 400px) {
  .my-reg-ex-container {
    width: 220px;
  }
}
.my-reg-ex-container .my-reg-ex {
  width: 100%;
  border-radius: 10px;
  border: 2px solid #f7ce51;
  box-shadow: 0 4px 20px rgba(245, 205, 81, 0.4);
  color: #f7ce51;
  background: transparent;
  outline: none;
  font-size: 24px;
  padding: 16px;
  border-radius: 12px;
  transition: all 0.5s ease-out;
  opacity: 0;
  transform: translateY(-20px);
}
@media (max-width: 400px) {
  .my-reg-ex-container .my-reg-ex {
    padding: 8px;
  }
}
.my-reg-ex-container.active .my-reg-ex {
  opacity: 1;
  transform: translateY(0);
}

.tabs {
  width: 100%;
  display: flex;
  justify-content: center;
  align-items: center;
  position: relative;
}
.tabs .slider {
  position: absolute;
  left: 0;
  bottom: 0;
  height: 100%;
  width: 33.33333%;
  background: linear-gradient(45deg, rgb(245, 205, 81) 0%, rgb(247, 206, 81) 100%);
  box-shadow: 0 4px 20px rgba(245, 205, 81, 0.4);
  border-radius: 9px;
  z-index: 0;
  transition: all 0.3s linear;
}
.tabs .tab {
  width: 50%;
  height: 100%;
  display: block;
  text-align: center;
  cursor: pointer;
  padding: 16px 0 16px 0;
  border-radius: 9px;
  font-size: 16px;
  z-index: 1;
  position: relative;
  color: #7c828d;
  transition: all 0.3s linear;
}
.tabs .tab:hover {
  color: #f7ce51;
}
.tabs .tab .title {
  font-size: 16px;
}
@media (max-width: 400px) {
  .tabs .tab .title {
    font-size: 14px;
  }
}
.tabs .tab.active .title {
  font-weight: 900;
  color: hsl(225, 14%, 12%);
}
.tabs .tab:nth-of-type(1).active ~ .slider {
  left: 0;
}
.tabs .tab:nth-of-type(2).active ~ .slider {
  left: 33.33333%;
}
.tabs .tab:nth-of-type(3).active ~ .slider {
  left: 66.6666%;
}

.jssecrets {
  font-weight: 500;
  text-decoration: none !important;
  font-family: "Urbanist";
  padding: 16px;
  background: #ffc805;
  color: #000000;
  font-size: 1.2em;
  letter-spacing: 0.2px;
  border-radius: 8px;
  box-shadow: 0px 4px 12px rgba(184, 144, 0, 0.1882352941), 0px 8px 24px rgba(184, 144, 0, 0.3764705882);
  position: absolute;
  bottom: 24px;
  right: 24px;
  transition: all 0.3s;
}

.jssecrets:hover {
  transform: translateY(-4px);
}
!

JS 

              
                // Variables
const tabs = document.querySelectorAll('.tabs .tab');
const input = document.querySelector('.primary');
const myRegExInput = document.querySelector('.my-reg-ex');
const myRegExContainer = document.querySelector('.my-reg-ex-container');

// Regular Expressions

// digits only
let regex = /\d/;
// any character
let myRegEx = /./;

// Functions
// 1. Set active tab
const setActiveTab = (event) => {
  // sliding tabs functionality
  document.querySelector('.tab.active').classList.remove('active');
  event.currentTarget.classList.add('active');
  //

  // clear input
  input.value = '';

  if (event.currentTarget.classList.contains('digits')) {
    // allow digits only
    regex = /\d/;
    // hide custom regex input
    myRegExContainer.classList.remove('active');
  } else if (event.currentTarget.classList.contains('letters')) {
    // allow uppercase and lowercase letters only
    regex = /[A-Za-z]/;
    // hide custom regex input
    myRegExContainer.classList.remove('active');
  } else {
    // allow allow any character
    regex = myRegEx;
    // show custom regex input
    myRegExContainer.classList.add('active');
  }
};

// 2. Input filter
const inputFilter = (event, regEx) => {
  // catch pressed key's code
  // and convert it to an actual character
  let symbol = String.fromCharCode(event.keyCode);

  // if character doesn't belong to regEx set
  // then prevent it from being typed
  if (!regEx.test(symbol)) {
    event.preventDefault();
  }
};

// 3. Input event
const inputEvent = (event) => {
  inputFilter(event, regex);
};

// 4. Setting user's input filter
const inputUserChoice = (event) => {
  // create and assign user's input to regEx
  myRegEx = new RegExp(`[${event.currentTarget.value}]`);
  regex = myRegEx;
};

// 5. Emptiness validation
const ifEmpty = (event) => {
  // custom regEx is empty
  // then allow any character
  if (
    !event.currentTarget.value.trim().length ||
    event.currentTarget.value === ''
  ) {
    regex = /./;
  }
};

// Event Listeners
// sliding tabs event
tabs.forEach((tab) => {
  tab.addEventListener('click', setActiveTab);
});
// input event
input.addEventListener('keypress', inputEvent);
// user's regEx
myRegExInput.addEventListener('input', inputUserChoice);
// check whether empty on blur
myRegExInput.addEventListener('blur', ifEmpty);
!
999px

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