<div class="access">
  <input
         type="password"
         class="access__password-field"
         placeholder="Введите пароль (123)">
</div>

<div class="header">
  <div class="header__container">
    <h1 class="header__logo">TJ</h1>
  </div>
</div>

<div class="sidebar">
  <div class="sidebar__container">
    <div class="sidebar__live">
      Прямой эфир
    </div>
  </div>
</div>

<div class="main">
  <div class="main__container">
    <div class="big-block"></div>
    <div class="big-block"></div>
    <div class="big-block"></div>
    <div class="big-block"></div>
    <div class="big-block"></div>
    <div class="big-block"></div>
    <div class="big-block"></div>
  </div>
</div>
body {
  margin: auto;
  background-color: #f0f0f0;
  font-family: sans-serif;
}

* {
  box-sizing: border-box;
}

.header {
  height: 60px;
  background-color: #fff4e2;
  width: calc(100% - 300px);
  position: fixed;
  left: 0;
  top: 0;
}

.header__container {
  width: 100%;
  height: 100%;
  display: flex;
  align-items: center;
  padding: 0 10px;
}

.header__logo {
  font-size: 1.5em;
  margin: 0;
}

.sidebar {
  width: 300px;
  background-color: #fff;
  min-height: 100vh;
  position: fixed;
  right: 0;
  top: 0;
}

.sidebar__container {
  width: 100%;
  height: 100%;
  display: flex;
  justify-content: center;
  flex-direction: column;
}

.sidebar__live {
  padding: 15px;
  text-align: center;
  border-bottom: 1px solid #ddd;
}

.main {
  margin-top: 80px;
  width: calc(100% - 300px);
}

.main__container {
  max-width: 90%;
  margin: auto;
}

.big-block {
  height: 50vh;
  background-color: #ccc;
  margin-top: 5px;
  border-radius: 3px;
  border: 1px solid #ddd;
}

.access {
  position: fixed;
  z-index: 999;
  background-color: #000;
  color: #999;
  opacity: 0.9;
  width: 100%;
  height: 100%;
  top: 0;
  left: 0;
  display: flex;
  align-items: center;
  justify-content: center;
}


.access__password-field {
  display: block;
  background-color: transparent;
  border: 1px solid #fff;
  color: #999;
  padding: 15px 0;
  text-align: center
}
const password = "123";
const passwordField = document.querySelector('.access__password-field');
const accessBox = document.querySelector('.access');

passwordField.addEventListener('input', function (e) {
  if (this.value == password) {
    accessBox.remove();
  }
});

External CSS

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External JavaScript

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