discourse/app/assets/stylesheets/desktop/modal.scss

.d-modal {
  --modal-max-width: 600px;
  --modal-width: 30em; // set in ems to scale with user font-size
  --modal-min-width: 400px;
  &__container {
    max-width: var(--modal-max-width);
    min-width: var(--modal-min-width);
    .d-modal.-large & {
      max-width: 800px;
    }
    .d-modal.-max & {
      max-width: 90vw;
    }
  }
}
//legacy
// Hardcode to be the same as before for now. I would recommend not using bootbox, or finding a way so the html structure can be the same
.bootbox.modal {
  top: 50%;
  left: 50%;
  width: 610px;
  margin: -250px 0 0 -305px;
  .cancel {
    margin-left: 1em;
  }
}

.modal.in {
  animation: fade 0.25s;
  @media (prefers-reduced-motion) {
    animation-duration: 0s;
  }
}

.close {
  font-size: var(--font-up-3);
  text-decoration: none;
  &:visited {
    color: var(--primary-high);
  }
  cursor: pointer;
  &:hover {
    color: var(--primary);
  }
}

.modal {
  .category-chooser {
    width: 50%;
  }

  .modal-body.insert-link {
    input {
      min-width: 450px;
    }
  }
}

.choose-topic-modal {
  .modal-body {
    position: relative;
    min-height: 350px;
  }

  #choosing-topic {
    // prevents content from moving when user selects different move options 525px
    // is the same width we set on category edit modal
    width: 525px;

    p {
      margin-top: 0;
    }

    .radios {
      margin-bottom: 10px;
      display: flex;
      flex-direction: row;

      .radio-label {
        display: inline-block;
        padding-right: 15px;
      }
    }

    button {
      margin-top: 10px;
      display: block;
    }

    form {
      width: 95%;
      margin-top: 20px;

      .participant-selector {
        width: 100%;
      }

      div.ac-wrap {
        width: 100%;
        margin-bottom: 9px;
      }
    }
  }
}

.change-post-notice-modal {
  .modal-body {
    min-width: 450px;
  }
}

.create-invite-modal,
.create-invite-bulk-modal,
.share-topic-modal {
  .title {
    align-items: center;
    display: flex;

    .subtitle {
      margin-left: 0.5em;
    }
  }

  &.modal .modal-body {
    margin: 1em;
    padding: unset;
  }

  .modal-inner-container {
    width: 40em; // scale with user font-size
    max-width: 100vw; // prevent overflow if user font-size is enormous
  }
}